Arc spray method for manufacturing a dense layer

ABSTRACT

An arc spray method is proposed for manufacturing a dense layer on a substrate in which an electric voltage is applied to two electrically conductive spray wires and with which an arc is ignited between the spray wires, wherein a melt is generated from the spray wires in a melting region, with the melt being acted on by a fluid which transports the melt to the substrate where the melt is deposited for generating the layer. Oxidizable particles are supplied to the melt and are deposited on the substrate together with the melt; and after the end of the spraying, the oxidizable particles are at least partly oxidized to densify the layer.

The invention relates to an arc spray method for manufacturing a dense layer in accordance with the preamble of the independent method claim. The invention further relates to a dense layer which is manufactured in accordance with such a method.

Coatings which are manufactured by means of thermal spraying are frequently exposed to corrosive phenomena. For example, deck coatings on ships are very highly exposed to sea air containing salt water and are therefore particularly prone to corrosion damage. It is admittedly known to apply corrosion protection layers, for example in the form of special paints or coatings; however, in this respect the effect called subsurface corrosion frequently occurs where corrosion arises on the substrate beneath he coating. This corrosion can have the result that the coating—that is, for example, the protective paint or the thermally sprayed protective layer—flakes off the substrate. The cause of this subsurface corrosion can be natural damage to the protective coating through which the material causing the corrosion, e.g. salt water, reaches onto the substrate and results in corrosion there. It is, however, also possible that the material causing the corrosion penetrates the protective layer which is intact per se via capillary effects or via diffusion processes and thus reaches the substrate. The protective layer is therefore quasi not dense enough. This effect is in particular also promoted when the protective layer has a high roughness. A high roughness of the protective layer is, however, often desirable for safety reasons, for example on the deck of ships to minimize the risk of slipping for the ship's crew.

It is therefore an object of the invention to propose an inexpensive and simple method for manufacturing a dense layer on a substrate which allows a protection of the substrate located beneath the layer, in particular against corrosion. A corresponding dense layer should furthermore be provided by the invention.

The subjects of the invention satisfying this object are characterized by the independent claims of the respective category.

In accordance with the invention, an arc spray method is therefore proposed for manufacturing a dense layer on a substrate in which an electric voltage is applied to two electrically conductive spray wires and with which an arc is ignited between the spray wires, wherein a melt is generated from the spray wires in a melting region, with the melt being acted on by a fluid which transports the melt to the substrate where the melt is deposited for generating the layer. Oxidizable particles are supplied to the melt and are deposited on the substrate together with the melt; and after the end of the spraying, the oxidizable particles are at least partly oxidized to densify the layer.

Arc spraying, which is frequently also more precisely called wire arc spraying, is a thremal sparying process with which layers can be deposited on a substrate in an inexpensive and simple manner. The oxidizable particles supplied to the melt are at least partly oxidized after the spray process. The particles increase their volume by the oxidation and thus densify the layer and the layer is sealed. The substrate located beneath the layer can herewith be protected with very special efficiency, in particular also from corrosion. Since the particles are distributed in the whole layer, not only the surface of the layer is densified, but rather the total layer is sealed in its interior.

It has proven particularly favorable in practice if the oxidizable particles adopt a volume share of 3% to 20% of the volume of the layer.

In accordance with a first preferred process management, the oxidizable particles are admixed with the fluid before the fluid acts on the melt. The particles therefore impinge onto the melt region together with the fluid and transport the melt from there onto the substrate.

Another preferred process management consists of adding the oxidizable particles to the melt between the melt region and the substrate. In this variant, the oxidizable particles are therefore introduced into the “jet” downstream of the melt region, said jet transporting the melt to the substrate.

It is furthermore possible that the oxidizable particles are a component of at least one spray wire. The spray wire is then designed, for example as a hollow wire or a so-called “core wire”, i.e. the oxidizable particles are integrated into the spray wire.

A further possible process management consists of a third spray wire being provided which contains the oxidizable particles.

In a preferred embodiment, the oxidizable particles contain iron or zinc or aluminum or magnesium or alloys of these elements. These elements or their alloys can be oxidized particularly simply. With respect to iron, there are a plurality of oxidizable iron compounds or iron-based materials with an iron content of at least 50% by weight which are suitable for the method in accordance with the invention, for example iron-based material with chromium and/or aluminum. Elemental aluminum or magnesium or zinc are also suitable due to their easy oxidizability and the volume increase associated therewith. Oxidized aluminum powder thus, for example, has approximately three times the volume of the non-oxidized aluminum powder. Furthermore the alloy ZnAl 85/15 is suitable which contains 85% by weight zinc and 15% by weight Al. One criterion for the suitable choice of the oxidizable particles is that they have no pronounced tendency to form alloys with the spray material. It is namely very possible, albeit not necessary, that the oxidizable particles melt or are plasticized in the method in accordance with the invention and then solidify again when they have been applied to the substrate together with the melt. It is not desired in such cases that the oxidizable particles form alloys with the spray material and then, as the case may be, are no longer oxidizable or are at least no longer simply oxidizable. An exception from this can be possible if the oxidizable particles form easily oxidizable alloys or other compounds with components of the spray material. It can then naturally be directly exploited that the oxidizable particles are only generated in the spray process or that the oxidizable particles enter into compounds which in turn represent oxidizable particles.

It is a particularly simple possibility for the oxidizable particles to be oxidized by means of water.

The method in accordance with the invention is also in particular suitable for those applications in which the substrate is made of steel or has a surface of steel. The subsurface corrosion of the steel under the layer can in particular be at least efficiently inhibited or delayed if not actually fully and permanently prevented by the sealing of the layer or by the density of the layer.

A dense layer is furthermore proposed by the invention which is manufactured using a method in accordance with the invention.

The dense layer preferably has internal compressive stresses. These internal compressive stresses in the layer can be directly generated by the oxidization of the oxidizable particles because the volume increase associated with the oxidization results in the formation of internal compressive stresses which can considerably improve the durability or the adhesion of the layer on the substrate.

Further advantageous measures and preferred embodiments of the invention result from the dependent claims.

The invention will be explained in more detail in the following with reference to embodiments and to the drawing. There are shown in the schematic drawing, partly in section:

FIG. 1 the major parts of an arc spray apparatus for carrying out a first embodiment of the method in accordance with the invention;

FIG. 2 as FIG. 1, but for a second embodiment of the method in accordance with the invention;

FIG. 3 a spray wire for a further embodiment of the method in accordance with the invention; and

FIG. 4 a schematic representation for clarification of a further embodiment.

FIG. 1 shows in a schematic representation the major parts of an arc spray apparatus which is suitable for carrying out a first embodiment of the method in accordance with the invention and with which a dense layer 18 can be manufactured on a substrate 10.

The arc spray apparatus includes a spray gun 1, a first supply device 3, a storage container 12 for oxidizable particles 11 which are usually present in the storage container 12 in powder form, and a control unit 14 to control the process. The spray gun 1 includes in a manner known per se two electrically conductive spray wires 2 which are connected to an energy source 16 for supply with electric energy so that an arc 6 can be ignited between the spray wires 2 in a melt region 7 and can be maintained in a stable manner over a predefinable period of time. The spray wires 2 can be supplied from a storage device, not shown, of a wire guide 5. The wire guide 5 includes a wire feed 13 which is suitable to supply the spray wire 2 through a guide device 17 to the melt region 7. The guide device 17 is preferably designed so that it can be connected to the energy source 16 as an electrically conductive device and is in electrically conductive contact with the spray wire 2 so that the electric energy required for the generation of the arc 6 can be supplied to the spray wire 2 via the guide device 17. Since material of the spray wire 2 is moved continuously into a melt 8 on arc spraying in the melt region 7, the spray wire 2 has to be fed continuously into the melt region 7 by the wire guide 5 to maintain the arc 6.

The arc spray method can, but does not have to, be carried out under a controlled atmosphere. In this case, the method is carried out in a process chamber 30, which is only indicated in FIG. 1 and whose atmosphere can be set or monitored in a manner known per se using pumps and gas supply devices, not shown.

The melt 8 formed from the material of the spray wire 2 in the arc 6 is acted on by a fluid 4 which is supplied from a gas store 19 via the first supply device 3. The fluid 4 transports the melt 8 onto a surface 9 of the substrate 10 to be coated, whereby the layer 18 is formed. The melt 8 is acted on at a predefinable working pressure by the fluid 4 which is preferably a gas, in particular oxygen, nitrogen, argon, helium, environmental air, a mixture of these or another gas, whereby the melt 8 is hurled onto the surface 9 of the substrate 10. The melt 8 condenses into a solid state there.

In accordance with the invention, the oxidizable particles 11 are supplied to the melt 8 such that the oxidizable particles 11 are deposited on the substrate 10 together with the melt 8. For this purpose, in accordance with the first embodiment described here, the oxidizable particles 11 are admixed t the fluid 4 before the fluid 4 acts on the melt 8.

For this purpose, a connection 15 is provided by which the oxidizable particles 11 can move out of the storage container 12 into the supply device 3 where they are taken along by the fluid 4 so that the particles 11 act on the melt 8 in the melt region 7 together with the fluid 4. The oxidizable particles 11 are thus supplied to the melt 8 by the fluid 4 so that the particles 11 are mixed with the melt 8 in the melt region 2 and are applied to the surface 9 of the body 10 together with the melt 8.

In this process, the oxidizable particles 11 can be partially melted or melted or plasticized. In this case, the material for the particles 11 should preferably be selected so that there is not any substantial formation of an alloy or compound between the particles 11 and the material of the spray wires 2. It is, however, also possible that the oxidizable particles 11 remain substantially solid and dimensionally stable during their transport in the melt 8. The particles 11, which are usually solid particles, are therefore then not melted in the melt 8 itself, but rather retain their external shape and remain substantially solid. It is naturally possible that only a slight partial melting of the particles 11 occurs at their surface.

After the end of the thermal spray process, the oxidizable particles 11 are oxidized in the layer 18. This takes place by being acted on by an oxidation means. A possible oxidation means is water. This can, for example, be sprayed onto the layer 18 or the layer 18 or the substrate 10 with the layer 18 can be brought into an immersion bath. Different oxidation means than water can naturally also be used. The volume of the oxidizable particles 11 increases in comparison with the non-oxidized state due to the oxidation; the particles 11 therefore quasi swell, whereby pores, capillary passages or other openings or passages in the layer 16 are closed or filled. The layer 18 is thus sealed by this oxidation. This sealing does not only take place at the surface of the layer 18, but also everywhere in the layer 18. This has the consequence that subsequently practically no liquids can penetrate the layer 18 any more so that the substrate 10 is very efficiently protected, in particular also from subsurface corrosion. Since the sealing or the densification takes place in the whole layer 18, it is possible to design the surface of the layer 18 rough without compromises in quality. This is, for example, advantageous as protection against slipping when the layer 18 is a surface, e.g. a ship's deck, on which persons walk.

A further advantageous measure which can be realized by the volume increase in the particles 11 is the generation of internal compressive stresses 18. The compression stresses are generated in the layer 18 by the swelling up of the particles 11 on the oxidation and have a positive effect on the durability or the adhesion of the layer 18.

If it is desired that the oxidizable particles 11 do not melt during the spray process, the shape stability of the particles 11 in the melt 8 can be ensured by some parameters; on the one hand, naturally by a suitable selection of the material for the particles 11, on the other hand, by the size of the particles 11 or by the flow rate of the fluid 11. A melting of the particles 11 can naturally also be realized by the same parameters.

A great number of materials, in particular in the form of solid body particles, are suitable as oxidizable particles 11 which serve for the subsequent densifying of the layer 18. There are suitable, for example: zinc, aluminum, magnesium, iron or alloys of these elements among one another or with other elements. In particular iron-based compounds having an iron content of more than 50% are suitable or also the alloy ZnAl 85/15 which contains 85% zinc and 15% iron.

To control or regulate the process, the arc spray apparatus has, for example, a freely programmable control unit 14 with which in particular the following parameters can be regulated or set: the working pressure at which the fluid 4 acts on the melt 8, the supplied quantity of particles 11, the wire feed 13, the electric energy supplied to the spray wires 2. For this purpose, the control unit 14 is connected to the respective components of the apparatus via signal lines 20. Furthermore, the control unit 14 can include sensor lines 21 by which different operating parameters such as current working pressure, gas pressure in the process chamber, environmental pressure, temperature electrical operating parameters of the energy source or other parameters can be communicated to the control unit 14 by sensors, not shown.

To manufacture the dense layer 18, the melt 8 generated in the melt region 7 by means of the arc spray process is now first transported by the fluid flow charged with the particles 11 to the surface 9 of the substrate 10 where the melt 8 is deposited in the form of splashes or droplets. The oxidizable particles 11, which are present in the form of solid particles or in a partially melted or melted form, are integrated into the layer 18 which forms. When the desired layer thickness has been reached, the thermal spray process is ended. In a further processing step, the oxidizable particles 11 are now oxidized in the solidified layer 18, whereby the layer 18 is sealed.

FIG. 2 shows the major parts of an arc spray apparatus for carrying out a second embodiment of the method in accordance with the invention. Only the differences from the first embodiment will be looked at in the following. The preceding explanations with respect to the first embodiment also apply in accordingly the same manner to the second embodiment. The same reference numerals designate the same parts or parts which are equivalent in function as in the first embodiment.

The major difference from the first embodiment is that in the second embodiment the oxidizable particles 11 are only added after the melt region 7 in the direction of flow.

For this purpose, a second supply device 31 is provided by which the oxidizable particles 11 can be introduced from the storage container 12 into the melt 8, with here the entry of the particles 11 only taking place between the melt region 7 and the substrate 10. For this purpose, the second supply device 31 has an opening 32 which is arranged in the vicinity of the melt region 7, but at the substrate side of the melt region 7, so that the particles 11 can be introduced from there into the coating jet formed by the melt 8 and the fluid 4. The particles 11 can also be transported through the second supply device 31 with the aid of the fluid 4 in this embodiment. For this purpose, the second supply device 31 is connected, for example, to the gas store 19 or to a separate fluid store (not shown in FIG. 2).

The apparatus shown in FIG. 2 naturally also has an energy source 16 whose illustration has been dispensed with here for reasons of clarity.

The melt 8 formed from the material of the spray wire 2 in the arc 6 is also applied here, analog to the previously described embodiment, to the surface 9 of the substrate 10 by the fluid 4 via the first supply device 3 from a gas store 19. The oxidizable particles 11 move from the opening 32 into the melt 8 and are then transported to the substrate 10 together therewith.

In accordance with a further embodiment of the method in accordance with the invention, the oxidizable particles can also be provided in one or both of the spray wires 2. The spray wire 2 is then designed as a cored wire which additionally contains the oxidizable particles 11 beside the actual, for example metallic, coating material. FIG. 3 shows such a spray wire 2 in cross-section. In this embodiment, it is then no longer necessary additionally to supply the oxidizable particles 11 from a storage container as is shown in FIGS. 1 and 2. In this further embodiment, the oxidizable particles 11 are released on the melting of the spray wire 2 in the melt region 7 and then move to the substrate 10, transported by the fluid 4 together with the melt 8. The achieved volume portion of the particles 11 at the layer 18 can then be set via the relative portion of the particles 11 in the spray wire 2.

A further embodiment is illustrated schematically in FIG. 4. In this embodiment, at least one third spray wire 22 is provided which contains the oxidizable particles 11. This third spray wire 22 is introduced into the melt region 7 where its tip is brought to melting, whereby the oxidizable particles 11 are released in order then to be transported to the substrate 10 by the fluid 4 together with the melt 8. It is understood that a wire feed is also provided for the third spray wire 22. The third spray wire 22 can be supplied when live or dead. If the third spray wire 22 is live, it can selectively be switched as a cathode or as an anode. At least one further arc, for example, arises in this respect. It is, however, also possible to conduct the third spray wire while dead so that it only melts by the heat of the melting region which is generated by the arc between the two spray wires 2. 

1. An arc spray method for manufacturing a dense layer on a substrate, wherein an electric voltage is applied to two electrically conductive spray wires with which an arc is ignited between the spray wires, wherein a melt is generated from the spray wires in a melt region, wherein the melt is acted on by a fluid which transports the melt to the substrate where the melt is deposited for generating the layer, characterized in that oxidizable particles are supplied to the melt which are deposited on the substrate together with the melt; and in that the oxidizable particles are at least party oxidized for densifying the layer after the end of the spraying.
 2. The method in accordance with claim 1, wherein the oxidizable particles adopt a volume portion of 3% to 20% of the volume of the layer.
 3. The method in accordance with claim 1, wherein the oxidizable particles are admixed to the fluid before the fluid acts on the melt.
 4. The method in accordance with claim 1, wherein the oxidizable particles are added to the melt between the melt region and the substrate.
 5. The method in accordance with claim 1, wherein the oxidizable particles are a component of at least one spray wire.
 6. The method in accordance with claim 1, wherein a third spray wire is provided which contains the oxidizable particles.
 7. The method in accordance with claim 1, wherein the oxidizable particles contains at least one of iron, zinc, aluminum, magnesium and alloys of at least one of iron, zinc, aluminum and magnesium.
 8. The method in accordance with claim 1, wherein the oxidizable particles are oxidized by means of water.
 9. The method in accordance with claim 1, wherein the substrate is made of steel or has a surface of steel.
 10. A dense layer manufactured in accordance with a method in accordance with claim
 1. 11. The dense layer in accordance with claim 10 which has internal compressive stresses. 